{"id":7826,"date":"2018-07-30T13:16:07","date_gmt":"2018-07-30T19:16:07","guid":{"rendered":"https:\/\/www.coloradofloodthreat.com\/?p=7826"},"modified":"2018-08-02T09:51:56","modified_gmt":"2018-08-02T15:51:56","slug":"fto-07-30-2018-on-and-off-rainfall-threat-with-movement-of-the-upper-level-ridge","status":"publish","type":"post","link":"https:\/\/archive-coftb.dewberryanalytics.com\/?p=7826","title":{"rendered":"FTO 07-30-2018: On and Off Rainfall Threat with Movement of the Upper-Level Ridge"},"content":{"rendered":"<p>Issue Date: Monday, July 30th, 2018<br>\nIssue Time: 1:20PM MDT<br>\nValid Dates:&nbsp;7\/31&ndash; 8\/14<\/p>\n<p><a href=\"https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2018\/07\/FTO-20180730.png\"><img loading=\"lazy\" class=\"alignnone wp-image-7827\" src=\"https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2018\/07\/FTO-20180730.png\" alt=\"\" width=\"880\" height=\"150\"\/><\/a><\/p>\n<p>We start this FTO period with a break from the heavy rainfall and severe weather. The flow aloft remains northerly the next couple of days, which will pull in dry air from WY and MT as seen in the water vapor imagery below. This should limit the rainfall chances to the higher terrains and the overall coverage of storms will also be reduced. This is a much needed rainfall break for the eastern plains of Colorado who have just gotten hammered by heavy rain and severe weather since Friday. So for the next couple of days, expect the upper-level high to spin over the Great Basin and dry out the lower-levels. This will allow the high temperatures to bounce back a bit when compared to last week with some of the lower elevations in western Colorado reaching the 90Fs by Tuesday.<\/p>\n<p>Starting Wednesday, mid-level disturbances will start to increase as a <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;trough&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;An elongated area of relatively low atmospheric pressure; the opposite of a ridge.&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>trough<\/span> moves into the Pacific Northwest. By Thursday, there is a complete breakdown the riding pattern over Colorado and the upper-level flow becomes more <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;zonal&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;refers to the east-west direction; usually used to describe atmospheric flow that roughly follows lines of latitude&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>zonal<\/span>. Subtropical moisture will return to the state with the greatest moisture statewide on Friday. The <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;zonal&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;refers to the east-west direction; usually used to describe atmospheric flow that roughly follows lines of latitude&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>zonal<\/span> pattern will also push shortwaves through the state, which if timed correctly, will increase lift and coverage of PM thunderstorms. Event #1 will begin on Wednesday (over the Southeast Mountains) and pick up intensity to start next weekend with an Elevated flood threat.<\/p>\n<p>By Sunday, the ridge begins to build back to the west and there should be a temporary decrease in available subtropical moisture and downtick in thunderstorm activity. <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;convection&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;Refers to vertical atmospheric motion driven by buoyancy, i.e., warm air is less dense than cool air, and therefore rises. One of the primary drivers of thunderstorm development, especially during monsoon season.&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>Convection<\/span> will still be likely over the higher terrains in the afternoon, but coverage will be greatly reduced. By Monday, the upper-level ridge begins to shift west with another upper <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;trough&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;An elongated area of relatively low atmospheric pressure; the opposite of a ridge.&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>trough<\/span> moving over the Pacific Northwest. If this occurs, this would allow for an influx of subtropical moisture first over western Colorado and then eastern Colorado by Tuesday (Event #2). Confidence is a bit lower in this solution as it is still over a week away.<\/p>\n<p style=\"text-align: center;\"><a href=\"https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2018\/07\/wv-20180730.png\"><img loading=\"lazy\" class=\"alignnone wp-image-7828 size-full\" src=\"https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2018\/07\/wv-20180730.png\" alt=\"\" width=\"625\" height=\"473\"\/><\/a><\/p>\n<p>A weak front is forecast to pass through the state on Wednesday, which will increase low-level moisture over the eastern portion of the state. <span class=\"glossaryLink\"  aria-describedby=\"tt\"  data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;PW&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;(Stands for: Precipitable Water) The total atmospheric water vapor contained in a vertical column of the atmosphere. It is typically measured in inches, and anomalously (deviation from normal) high values of precipitable water generally correlate to heavy rainfall potential.&lt;\/div&gt;\"  data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>PW<\/span> is expected to rise the most over the southeast corner of the state on Wednesday, which could return the flood threat to the Southeast Mountain and in particularly, the recent burn scars. Thursday into Friday, <span class=\"glossaryLink\"  aria-describedby=\"tt\"  data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;PW&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;(Stands for: Precipitable Water) The total atmospheric water vapor contained in a vertical column of the atmosphere. It is typically measured in inches, and anomalously (deviation from normal) high values of precipitable water generally correlate to heavy rainfall potential.&lt;\/div&gt;\"  data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>PW<\/span> continues to increase and by Friday, <span class=\"glossaryLink\"  aria-describedby=\"tt\"  data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;PW&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;(Stands for: Precipitable Water) The total atmospheric water vapor contained in a vertical column of the atmosphere. It is typically measured in inches, and anomalously (deviation from normal) high values of precipitable water generally correlate to heavy rainfall potential.&lt;\/div&gt;\"  data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>PW<\/span> will reach its maximum both east and west of the <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;Divide&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;&amp;lt;!-- wp:paragraph {&amp;quot;textColor&amp;quot;:&amp;quot;white&amp;quot;} --&amp;gt;\n&amp;lt;p class=&amp;quot;has-white-color has-text-color&amp;quot;&amp;gt;the dividing line that separates the watersheds of the western and eastern United States; rivers west of the divide empty into the Pacific Ocean, while rivers east of the divide empty into the Atlantic Ocean or Gulf of Mexico&amp;lt;\/p&amp;gt;\n&amp;lt;!-- \/wp:paragraph --&amp;gt;&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>divide<\/span>. Over western Colorado, the moisture seems to make a run much further north, so the rainfall is expected over the Northern and Central Mountains with the Central Mountains being included in the flood threat on Friday. After Friday, the GEFS ensemble shows some spread in the <span class=\"glossaryLink\"  aria-describedby=\"tt\"  data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;PW&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;(Stands for: Precipitable Water) The total atmospheric water vapor contained in a vertical column of the atmosphere. It is typically measured in inches, and anomalously (deviation from normal) high values of precipitable water generally correlate to heavy rainfall potential.&lt;\/div&gt;\"  data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>PW<\/span> plumes, as there is less confidence as to where the ridge will set up this far out. Likely, moisture will remain high over eastern Colorado and decrease to the west as the ridge begins to build over the southwest again.<\/p>\n<p><a href=\"https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2018\/07\/pw_plumes_20180730.png\"><img loading=\"lazy\" class=\"alignnone wp-image-7829\" src=\"https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2018\/07\/pw_plumes_20180730.png\" alt=\"\" width=\"880\" height=\"306\"\/><\/a><\/p>\n<p>Below we describe the two identified precipitation event of this FTO in more detail.<\/p>\n<h3><strong>Event #1: <\/strong><strong>Wednesday<\/strong><strong> (<\/strong><strong>8\/1<\/strong><strong>) &ndash; <\/strong><strong>Saturday<\/strong><strong> (<\/strong><strong>8\/4<\/strong><strong>)<\/strong><\/h3>\n<p><span style=\"color: #ff6600;\"><strong>Elevated Threat<\/strong><\/span><strong><span style=\"color: #0000ff;\"> \/ No Apparent Threat<\/span>&nbsp;<\/strong>as the ridge breaks down and <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;zonal&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;refers to the east-west direction; usually used to describe atmospheric flow that roughly follows lines of latitude&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>zonal<\/span> flow returns upper-dynamics and subtropical moisture.<\/p>\n<p>After rotating over the desert southwest and drying out the lower-levels, the upper-level high will begin to break down as a <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;trough&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;An elongated area of relatively low atmospheric pressure; the opposite of a ridge.&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>trough<\/span> moves north of Colorado. This should allow subtropical moisture to return to the state, as well as allow multiple mid-level shortwaves to pass through the state and increase thunderstorm coverage. Friday, <span class=\"glossaryLink\"  aria-describedby=\"tt\"  data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;PW&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;(Stands for: Precipitable Water) The total atmospheric water vapor contained in a vertical column of the atmosphere. It is typically measured in inches, and anomalously (deviation from normal) high values of precipitable water generally correlate to heavy rainfall potential.&lt;\/div&gt;\"  data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>PW<\/span> and the flood threat looks to the highest with chances for showers and thunderstorms both east and west of the <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;Continental Divide&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;&amp;lt;!-- wp:paragraph {&amp;quot;textColor&amp;quot;:&amp;quot;white&amp;quot;} --&amp;gt;\n&amp;lt;p class=&amp;quot;has-white-color has-text-color&amp;quot;&amp;gt;the dividing line that separates the watersheds of the western and eastern United States; rivers west of the divide empty into the Pacific Ocean, while rivers east of the divide empty into the Atlantic Ocean or Gulf of Mexico&amp;lt;\/p&amp;gt;\n&amp;lt;!-- \/wp:paragraph --&amp;gt;&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>Continental Divide<\/span>. Storm motion also looks to decrease at this time, which would allow more rain to fall over one area. This also means an increased risk for mud flows and debris slides over the recent burn scars. Decent <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;CAPE&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;(Stands for: Convective Available Potential Energy) CAPE is a measure of the amount of available energy in the atmosphere for convection. Higher values indicate a greater potential for stronger updrafts, thus an increase in the potential for thunderstorms and severe weather.&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>CAPE<\/span> and <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;shear&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;Local variation of the wind, either in the horizontal or vertical direction.&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>shear<\/span> will be in place over the far eastern plains on Friday and Saturday, so storms that form or move into this environment may become severe. The main threats would be local, heavy rainfall, large hail and strong winds. The daily details for this period will be monitored closely in the FTB as the far eastern plains could remain <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;capped&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;The area where a parcel of air has negative buoyancy or sinks. The intensity of the cap is measured by its convective inhibition. If the cap is sufficiently large, it may prevent thunderstorms from forming at all.&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>capped<\/span>.<\/p>\n<div style=\"position: relative;\"><a href=\"https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2018\/07\/FTO_20180730_e1_snap.png\"><img loading=\"lazy\" class=\"alignnone wp-image-7864\" src=\"https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2018\/07\/FTO_20180730_e1_snap.png\" alt=\"\" width=\"880\" height=\"496\"\/><\/a><\/div>\n<p><a href=\"https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2015\/05\/Legend.png\"><img loading=\"lazy\" class=\"alignnone size-full wp-image-230\" src=\"https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2015\/05\/Legend.png\" alt=\"Legend\" width=\"94\" height=\"158\"\/><\/a><\/p>\n<h3><strong>Event #2: <\/strong><strong>Monday<\/strong><strong> (8\/<\/strong><strong>6<\/strong><strong>) &ndash; <\/strong><strong>Thursday<\/strong><strong> (8\/<\/strong><strong>9<\/strong><strong>) <\/strong><\/h3>\n<p><strong><span style=\"color: #0000ff;\">No Apparent Threat<\/span>&nbsp;<\/strong>as upper-level ridge moves east and allows for subtropical moisture to return to the state.<\/p>\n<p>Less confidence in the forecast due to it being over a week away, but the models are currently digging another <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;trough&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;An elongated area of relatively low atmospheric pressure; the opposite of a ridge.&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>trough<\/span> through the Pacific Northwest. This would push the upper-level ridge east of Colorado, which is a classic pattern that returns subtropical moisture first to the western portion of the state and then to the eastern portion of the state. Thus, the flood threat would return for the showers and thunderstorms that form under the diurnal flow. With the ridge so far north, steering winds are also expected to decrease, so heavy rainfall would be expected. Please return back to the FTO on Thursday as it is likely many details of this forecast will change.<\/p>\n<p>&nbsp;<\/p>\n<div style=\"position: relative;\"><a href=\"https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2018\/07\/FTO_20180730_e2_snap.png\"><img loading=\"lazy\" class=\"alignnone wp-image-7865\" src=\"https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2018\/07\/FTO_20180730_e2_snap.png\" alt=\"\" width=\"880\" height=\"500\"\/><\/a><\/div>\n<p><a href=\"https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2015\/05\/Legend.png\"><img loading=\"lazy\" class=\"alignnone size-full wp-image-230\" src=\"https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2015\/05\/Legend.png\" alt=\"Legend\" width=\"94\" height=\"158\"\/><\/a><\/p>","protected":false},"excerpt":{"rendered":"<p>Issue Date: Monday, July 30th, 2018 Issue Time: 1:20PM MDT Valid Dates:&nbsp;7\/31&ndash; 8\/14 We start this FTO period with a break from the heavy rainfall and severe weather. The flow aloft remains northerly the next couple of days, which will pull in dry air from WY and MT as seen in the water vapor imagery [&hellip;]<\/p>","protected":false},"author":8,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[3],"tags":[],"post_mailing_queue_ids":[],"_links":{"self":[{"href":"https:\/\/archive-coftb.dewberryanalytics.com\/index.php?rest_route=\/wp\/v2\/posts\/7826"}],"collection":[{"href":"https:\/\/archive-coftb.dewberryanalytics.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/archive-coftb.dewberryanalytics.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/archive-coftb.dewberryanalytics.com\/index.php?rest_route=\/wp\/v2\/users\/8"}],"replies":[{"embeddable":true,"href":"https:\/\/archive-coftb.dewberryanalytics.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=7826"}],"version-history":[{"count":2,"href":"https:\/\/archive-coftb.dewberryanalytics.com\/index.php?rest_route=\/wp\/v2\/posts\/7826\/revisions"}],"predecessor-version":[{"id":7866,"href":"https:\/\/archive-coftb.dewberryanalytics.com\/index.php?rest_route=\/wp\/v2\/posts\/7826\/revisions\/7866"}],"wp:attachment":[{"href":"https:\/\/archive-coftb.dewberryanalytics.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=7826"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/archive-coftb.dewberryanalytics.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=7826"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/archive-coftb.dewberryanalytics.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=7826"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}